An aerosol typically is comprised of finely divided particles of a liquid and/or solid and is useful in a wide variety of applications. An aerosol can be used to administer a medicament, for example, by being inhaled into the lungs of an animal or human. Other applications of aerosols include, for example, instrument calibration, inhalation toxicology studies, air filter testing, nuclear safety analysis, and the delivery of scented materials, paints and lubricants.
In the delivery of a medicament to the lungs of an animal or human, the location in the lungs which should be treated with such a medicament at least depends on the type of ailment being treated and the type of medicament being used. The particle size distribution and the uniformity of an aerosol typically control or contribute to the location at which the aerosol particles settle in the lungs. As used herein, the term “particle size distribution” relates to the mass distribution of a material over a range of particle sizes of the material. The uniformity of an aerosol relates to the degree of dispersion of the mass distribution of a material over a range of particle sizes of the material.
Providing aerosol particles having an excessively large particle size distribution can have an adverse effect on the administration of the medicament. For example, aerosol particles having large particle size distributions can be deposited in the mouth and/or pharynx of a recipient, rather than inhaled into the lungs. On the other hand, providing aerosol particles having an excessively small particle size distribution can also have an adverse effect on the administration of the medicament, for example, because such small particles are sometimes exhaled prior to settling in the lungs.
Providing aerosol particles having an excessively broad range of particle sizes can have an adverse effect on the administration of the medicament. For example, aerosol particles with an excessively broad range of particle sizes are generally deposited throughout the lung or multiple parts of the lung, rather than a specific site in the lung. Thus, to effectively deposit a medicament in the lungs, it can be important to obtain an aerosol having a predetermined and sufficiently uniform particle size distribution which is suitable for treating a particular ailment using a particular medicament.
The particle size distribution of an aerosol or a component that is present in the aerosol can be measured by determining the mass median aerosol diameter (MMAD) thereof. The MMAD of an aerosol is the mass median diameter of the aerosol particles. The MMAD of a component present in an aerosol is the mass median diameter of the aerosol particles containing the component to be measured.
As discussed above, the uniformity of a particle size distribution can also affect the placement of the aerosol deposition in the lungs. The uniformity of a particle size distribution of an aerosol or a component that is present in the aerosol can be measured by determining the geometric standard deviation (GSD) thereof. The GSD of an aerosol or a component that is present in the aerosol is calculated as the ratio of the observed particle size at the 84th percentile divided by the observed particle size at the 50th percentile on a cumulative percent mass undersize distribution. The terms “monodispersed” and “polydispersed” as used herein relate to the uniformity of the particle size distribution of the aerosol. The lower the GSD is of an aerosol, the more “monodispersed” the particle size distribution is. Similarly, the higher the GSD is of an aerosol, the more “polydispersed” the particle size distribution is. For example, monodispersed particle size distributions typically include aerosols having a GSD of about 2 or less and polydispersed particle size distributions typically include aerosols having a GSD of about 3 or more.
In view of the foregoing, it is desirable to provide a means for achieving a predetermined and/or substantially monodispersed particle size distribution of an aerosol. It is also desirable to provide a means for achieving a sufficiently small particle size distribution of an aerosol which allows for the deep penetration of the aerosol into the lungs and for the treatment of an ailment requiring such deep penetration. It is further desirable to provide a means for achieving a sufficiently large particle size distribution which allows for the central deposition of the aerosol into the lungs and for the treatment of an ailment requiring such central deposition. One or more of these attributes can be achieved by the methods described herein.